(1) FIELD OF THE INVENTION
The invention relates to the general field of pressure valves, more particularly air activated pressure valves, and the in-situ monitoring of their performance.
(2) DESCRIPTION OF THE PRIOR ART
Air activated pressure valves are widely used for the control of fluid flow. The basic unit consists of a flow valve, such as a butterfly valve, suitable for use with fluids such as nitrogen or argon gas. The valve is activated by remote control by means of compressed dry air (CDA). This method for adjusting the rate of flow through fluid valves is preferred to electrically controlled valves since the mechanism that is involved is cheaper and more compact than a solenoid, as well as being less susceptible to possible corrosion by the fluid concerned.
A number of sophisticated (and hence expensive) systems have been described for use in controlling fluid flow. Of particular interest are the systems in which the necessary sensors are located within the valve mechanism itself. These systems could conceivably be used to also check on the functionality of the pressure valves but, if that were their sole purpose, they would represent a case of overkill, particularly in systems containing large numbers of pressure valves each of which needs to have its performance checked, either continuously or as desired. Under these circumstances, it is important to be able to use a checking system that has minimum cost.
An example of a full fledged control system for an air activated pressure valve is that described by Haines et al. in U.S. Pat. No. 5,251,148 (October 1993). This system includes pressure sensors (as opposed to pressure switches) located inside both the inlet and outlet chambers. The outputs from these pressure sensors are used to continuously control a throttle (valve plug) by means of a suitable actuator mechanism. In order for this device to operate it is necessary to measure the position of the valve plug, the valve inlet pressure, the valve outlet pressure, and the valve fluid temperature.
Given these measurements, the associated electronics of the Haines et al. system are then used to compute several (typically 9) numerical quantities the final result being used to determine the best current position for the valve plug.
A similar system (in the sense of being sophisticated, precise, and expensive) has been described by Lenz et al. (U.S. Pat. No. 5,558,115 September 1996). The heart of their system is a feedback loop between the inlet and outlet pressure sensors. This allows dynamic correction of unintended changes in fluid flow rates and also provides diagnostic information in the event of malfunction.
The present invention is concerned with monitoring pressure valve performance rather than controlling fluid flow.